Manufacture of vacuum-tube devices.



H. D. ARNOLD.

MANUFACTURE OF VACUUM TUBE DEVICES.

APPLICATION FILED NOV-1B 1915.

Patented Mar. 18, 1919.

' lnvenlor: limo/n Arno/d HAROLD D. ARNOLD, or EAsT ORANGE, NEW JERSEY, AssIcNOR, RY MESNE AssreN- NENTs, To WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OE NEW YORK.

MANUFACTURE OF VACUUM-TUBE DEVICES.

Specification of Letters ratent. I

Patented Mar. 18,1919.

Application filed November 18, 1915. Serial No. 62,259.

the Manufacture of Vacuum-Tube Devices,

of which the following is a full, clear, concise, and exact description.

This invention relates to the manufacture of vacuum tube devices, and more particularly it relates to a method of exhausting air and other gases and vapors from the glass bulbs or containers which inclose the electrode elements of thermionic repeaters, such as audions, and slmllar devices 111. whlch extremely high vacua are deslred.

Its objects are an effectively complete elimination of the gases occluded by the walls of the containing vessel, and bythe electrode elements and other metallic sur-* faces inclosed therein, a removal of such gases or any other gases from the containing vessel, and a resulting product characterized by stability and uniformity of operation.

To these ends this invention provides for the attachment of the vessel to be exhausted .to any suitable vacuum pump and for the application of heat to the exterior of such vessel during the process of evacuation. It further provides for the heating of one or more of the inclosed electrodes by the passage of an electric current therethrough, and

- repeater elements 2 ar'y' filamentary cathode 3, grid and an'o'd'e for the production in said vessel of an electron discharge which may be madeto bombard and heat another electrode through the application of a suitable potential difference between the said electrode and the source of said discharge.

A more complete understanding of the method of this invention will be obtained by consideration of the attacheddrawing, (which illustrates an apparatus arrangement suitable'for producing the high vacua desired in thermionic devices ofthe audion type. It will, of course, be appreciated that the method herein disclosed is equally applt;

cable to theproduction of high vacua'in any device having an electrode or electrodes capable of producing an electron discharge.

In the drawing, a plurality of thermionic each having the custom- 5, are'inclosed; in an oven 6 which may be electrically heated by a resistance element 7 connected to a suitable source of current 8. The glass containing-vessels 9 of the ole ments 2 have tubular extensions 10 connected to a main tube 11 leading to an exhaust apparatus 12, such, for example, as a Gaede molecular pump, connected to a source of motive power 13. The terminals of the electrode elements 3, 4; and 5 are brought out through suitable apertures 14in one of the walls of the oven 6, so as to be readily available for test purposes and for the application of any desired el'ectromotive force. A suitable number of windows 15 are provided in the front of the oven 6 so that the appearance of the tubes 2 being exhausted may be observed during the process. The filaments 3 are connected in series with a source of current 16 and a variable resistance 17. The I process of exhausting the vessels 9 is as fol- 7 5 lows: The pump 12 is started and the temperature of'the oven 6 is. gradually raised until it has reached approximately 350 C. The purpose of this'heating is to drive out the gases occluded by the walls of the vessel 9. After the temperature of the Oven has risen ,to. about 250 C., the filaments 3 are brought to incandescence by current supplied from the source 16, which current is raised to a value approximately 10% greater than the current normally to be used'in the operation of the completed device. A potential diflerence is thereupon successively applied to the terminals'of the electrodes 4 and 5 by means of a test clip 20 connected through the potentiometer 21 to a direct current source 22 of about 220 volts output. The

filament 3 being connected to the negative is attached, even to incandescence, which heating is eifective to drive out any gases 10 WlllCh may be occluded by said electrode.

The electron discharge, which passes from the cathode s to either electrdde 4 5"w'hen a potential diflerence is established therebetween, partially ionizes whatever gasm-ay be in its path. When gas in s'uflicient quantity is thus ionized, there will result a blue glow in part or all of the vessel 9, which may readily be observed through one of the windows 15. The intensity of this blue glow depends upon the amount of gas presentand upon the current and potential difference impressed between the cathode 3 and electrode 5. For-a given current and potential difference therefore, this blue glow will gradually become fainter as the gas within the vessel becomes more attenuated, until the glow finally disappears.

A visible indication of the sufficiency ofevacuation is therefore available, and, for example in exhausting the bulbs of thermionic repeaters, such as are employed in telephone work, it has been found that a sufficiently high vacuum has been obtained if the blue glow no longer appears, when approximately 175 volts potential difference is impressed between the cathode 3 and the anode 5. When this point has been reached, the tubes are allowed to cool gradually and are sealed off of the pump 12 and given an aging run, which consists in applying the normal heating current to the filaments 3 and impressing the customary operating potential difference between the cathode 3 and an-ode 5. It has been found that after an aging run of from fifteen to twenty hours durati-on, for example, therepeaters have reached a stable condition and may be relied upon to give constant and uniform results.

In case the thermionic device .to be exhausted is equipped with a grid 4 of very fine mesh, as in the case of a repeater deigned for voltage amplification, it may be diflicult-to obtain a current to the electrode 5 sufficient to heat it properly. In such an event, it has been found desirable to apply an additional positive potential from a source 23, for exampleof perhaps 60 volts output, to the grid electrode 4 at the same time that the positive. potential from source 22 is being applied to the anode 5. This increases the flow of electrons to the anode 5, and as some current will also flow between the filament 3 and grid 4, the voltages may be adjusted so as to heat both electrodes 4. and 5 at the same time. 7

With some tubes the early part "of the process may be accelerated by applying to 0th the grid electrode 4 and the anode 5 the same large potential as that which later in the process is applied to the anode only.

What is claimed is: e '1'. The method of producing a highvacuum in a thermionic discharge tube co-n't-aining three electrodes, which comprisesheating one of said electrodes and establishing an electron discharge between said heated electrode and a second one of said electrodes, whereby said second electrode is heatedduring the process of evacuation, and in assisting the passage of said discharge by means of a potential difference applied between the source of said discharge and the third electrode.

2. The method of producing a highvacuum in a thermionic discharge tube containing three electrodes, which comprises heating one of said electrodes to cause it to emit electrons, in establish-ing an electron discharge between said heatedelectrode and the other two electrodes during the process of evacuation, whereby said two electrodes are heated by bombardment and their occluded gases are driven off.

. 3. The method of evacuating a vacuum tube having cathode, anode and grid electrodes, which comprises energizing said cathode to cause it to emit electrons, in establishing an electron discharge between said 2cathode and said other electrodes during the evacuation, and in maintaining said grid at a potential different from that of said cathode during said discharge.

4. The method of evacuating a vacuum tube having cathode, anode and grid electrodes, which comprises energlzing said cathode to cause it to emit electrons, and in maintaining said grid and anode at a positive potential with respect to that of said cathode during evacuation.

In witness whereof, I hereunto subscribe my name this fifteenth day of November, A. D. 1915.

HAROLD D. ARNOLD. 

